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COMPLETED PROJECT

Project Products:

Scientific Investigations Report 2004-5286
Simulated Water-Level Responses, Ground-Water Fluxes, and Storage Changes for Recharge Scenarios along Rillito Creek, Tucson, Arizona
by John P. Hoffmann and S.A. Leake

Water-Resources Investigations Report 01-4257
Characteristics of Shallow Deposits Beneath Rillito Creek, Pima County, Arizona
by J.P. Hoffmann, M.A. Ripich, and K.M. Ellett

Development of methods to estimate ground-water recharge, Rillito Creek, Arizona

Project Number: AZ169
Project Chief: John Hoffmann
Cooperating Agencies: Arizona Department of Water Resources
Period of Project: COMPLETED

PROBLEM

Several artificial recharge sites are proposed for the Tucson region including one along a 12-mile reach of the Rillito Creek. Although infiltration of streamflow is known to occur in ephemeral channels in the Southwest, the process of recharge to underlying aquifers is poorly understood. Design of in-channel recharge facilities, without information that can be used to estimate performance and optimize design, comprises an expensive and uncertain venture.

OBJECTIVES

1. Evaluate the spatial and temporal aspects of the processes of recharge beneath Rillito Creek.
2. Estimate the potential for recharge along a 12-mile reach of Rillito Creek.
3. Estimate the benefit to the regional aquifer from various recharge scenarios.

APPROACH

The approach used to meet these objectives will include (1) the compilation and evaluation of existing data including well logs, water-level trends, streamflow records, infiltration data, and any other data deemed relevant, (2) the collection and analysis of geophysical data including borehole gamma and conductivity logs, and seismic refraction, electromagnetic, and resistivity surveys, (3) drill cuttings and cores will be collected at regular intervals during the drilling of five boreholes; cuttings and cores will be analyzed for selected environmental tracers and physical and hydraulic properties, (4) the development of saturated and unsaturated flow models of the study area. Once calibrated, these models will be used to simulate a series of in-channel recharge scenarios to determine which method of recharge would contribute the greatest amount of recharge to that part of the regional aquifer most susceptible to water-level declines and land subsidence.

RELEVANCE AND BENEFITS

The study will advance the understanding of ground-water flow through the unsaturated zone and provide defensible estimates of the timing and location of recharge on a subregional scale. The study will yield a simulation tool that can be used to examine natural and artificial recharge scenarios within the study area. It will facilitate evaluation of potential recharge and other water-related projects in the Rillito Creek channel. The geohydrologic information will provide a framework for subsequent geohydrologic and engineering investigations. The Rillito Creek is fast becoming an outdoor laboratory for research into recharge. Future recharge studies in other areas can be modeled after the Rillito Creek study.